1. Field of the Invention
The present invention relates to a process for the preparation of fireproof furniture hardwoods and for fireproofing wood products in general by utilizing a controlled permeation of a fire retardant solution composed of a combination of a halide salt of a Group I or Group II metal of the Periodic Table of Elements and an ammonium salt which after impregnation precipitates as an ammonium halide in the cellular structure of the treated wood. More particularly, the invention pertains to a process that is compatible with traditional furniture finishing techniques for manufacturing fireproof furniture utilizing a controlled permeation of a fire retardant solution in furniture hardwood by the evacuation and expansion of the cellular structure of the wood prior to the controlled impregnation of the surface of the treated wood to depths of about 1/8 of an inch to about 3 inches wherein the salts of the treating solution react and are deposited within the cellular structure of the treated wood.
2. Description of the Prior Art
A number of processes and treating compositions exists in the prior art for the treatment of wood and wood products for imparting fire resistance, preventing decay and insect proofing for softwood and softwood products utilized primarily in an exterior environment. In addition to pertaining to the treatment of softwoods the prior art does not utilize a controlled impregnation of the wood but instead relies upon various pitch or tar coatings as in the case of telephone poles or utilizes techniques designed to provide a saturation of the cellular structure to the core of the wood with the treating solution. Representative of processes for the treatment of softwoods for exterior applications are U.S. Pat. Nos. 3,159,503; 3,306,765 and 3,427,186.
In U.S. Pat. No. 675,826 a process for the fireproofing and preserving wood is disclosed wherein salts of zinc or magnesium are combined with ammonium salts to form new crystals and combinations that are much less soluble in water than either the magnesium or zinc salts and which are utilized to impregnate a more or less dry wood which is thereafter subjected to an ammoniacal atmosphere to convert the metallic salts in the wood to a greater or less extent to basic salts which are nearly insoluble in water, and finally into hydrates. Furthermore, in this patent a high vacuum is utilized along with a pressure of 150 psi on the impregnating solution which by the combined effect of vacuum and pressure forces the impregnation solution to the heart of the softwood which usually takes about 12 hours.
The prior art procedures for fireproofing softwoods by saturating the wood to the core are in marked contrast to the present invention for fireproofing hardwood products generally utilized in the furniture industry. Furthermore, the softwoods are structurally different from hardwoods in that softwoods are composed of tracheid and parenchyma cells which are generally more porous than hardwoods which are composed of vessel members, fibers and the more compact parenchyma cells. As a result of the difference in cellular structure, the softwoods have generally been more receptive to treatment with fluids whereas the hardwoods have generally resisted fireproofing treatments utilized in the prior art for softwoods. In addition, the procedures and fire retardant compounds heretofore employed are not compatible with finishing techniques employed for furniture and have severely interferred with the appearance of the grain and texture of the wood.
It has been discovered that in contrast to the prior art, fireproofing of hardwoods and softwoods alike may be accomplished by utilizing a controlled permeation of wood with a solution composed of a combination of a halide salt selected from a Group I or Group II metal of the Periodic Table of Elements and an ammonium salt which upon absorption and adsorption into the cellular structure of the wood reacts and precipitates as an ammonium halide in the treated wood. Controlled permeation of the fire resistant solution is accomplished by treating wood to depths from about 1/8 of an inch to about 3 inches where the diameter of the wood ranges from about 10 inches to 10 inches depending on the type of wood and does not utilize the complete saturation of the entire cellular structure to the core of the wood product. The present invention generally employs a surface penetration of the wood that constitutes a treatment of from about 5 to about 20% of the entire area of the fireproofed wood. It has been discovered that this surface treatment of wood in accordance with the invention is effective in fireproofing the exterior of the wood and protecting and insulating the internal core of the wood from the combination of heat and oxygen necessary for combustion. Treatment of hardwoods with the flame resistant process of the present invention provides an effective fire and smoke resistant product that withstands burning and smoldering in open flame and temperatures up to 2,000.degree. F.
The present process for the controlled permeation of a solution which is believed to react in the cellular structure of the wood product to provide a fire resistant wood is accomplished by expanding and evacuating the cellular structure of the wood to be treated by vacuum pressure, heating, or a combination of heat and pressure to activate the cellular structure of the wood prior to its impregnation with a fire retarding compound. Preferably, the fire resistant treatment of the invention is applicable to furniture wood products since the controlled permeation of the treating solution is compatible with high quality furniture to achieve the advantages of the invention due to the cellular structure of the wood, however, the invention is equally applicable to softwoods which require a higher percentage of permeation of treating solution in relation to the total diameter or thickness in view of the permeability of the cellular structure of the wood to oxygen, the relative flamability of the constituents in the cellular structure and the relative size of cells.
The prior art in contrast pertains to softwoods that are treated to the core utilizing impregnation procedures and fire retardant compositions that for the most part are not compatible with furniture manufacture. Furthermore, the prior art has employed steaming procedures or subjecting the softwoods to an atmosphere containing a high percentage of moisture to soften the cells and make them more pliable. The present invention in contrast employs dry wood and dry heat in attaining the advantages of the method and composition utilized in the invention. In addition, the prior art processes and flame retardant compounds have required the use of sophisticated pressure vessels and vacuum chambers to result in the impregnation and treatment of softwood products. Furthermore, some of the prior art procedures require the subsequent processing of the fire retardant compositions by utilizing drying kilns and chemical reaction in ammoniacal atmospheres for extended periods of time which further increase expense in processing and imposing corrosion resistance requirements for pressure and vacuum vessels.
The prior art processes for imparting flame resistance to wood further exhibits the disadvantage of requiring extended periods of time to introduce fire resistant compounds into the cellular structure of the wood which add increased expenditures in time, labor and material required to impart flame resistance to the wood products thereby causing treated woods to be much more expensive in comparison with untreated woods. The problems resulting from the pressure and vacuum conditions and the requirements for reduced fire, smoke and smoldering capacities of hardwood products generally employed in household furnishings and the inability of many of these processes and procedures to accommodate finishing procedures and techniques ordinarily employed in the furniture industry is considered as the reason for the failure of the prior art to provide a viable process for imparting flame resistance to furniture products.
The propagation of fire and deaths from fires is in part fostered by the combustability and the evolution of smoke by contemporary wood furnishings, particularly in cases where the building itself is fireproof. This is particularly apparent in dinner clubs, restaurants, mobile homes, hospitals and nursing homes where the use of furniture that would not burn would be justified regardless of cost. As a result there exist a requirement for an economical process for fireproofing hardwoods of the variety utilized in furniture which does not interfere with the visual appearance of the wood and is compatible with the finishing techniques generally employed in the manufacture of furniture.